Rosy leaf curling aphid (Dysaphis devecta (Walker))
Rosy leaf curling aphid damage
Rosy leaf curling aphid is a widely distributed but localised minor pest of apple.
Infestations occur on the same trees (often older trees with rough bark) year after year and spread from tree to tree is slow. The life cycle involves overwintering on the tree as eggs.
Some apple varieties, including Cox, Ashmead’s Kernal, Fiesta, Fortune, Gala, James Grieve, Kidd’s Orange Red, Lord Lambourne, Merton Worcester, Sunset, Suntan and Winston are resistant to rosy leaf curling aphid. Others, notably Elstar, Falstaff, Idared, Golden Delicious and Worcester Pearmain, are highly susceptible. Bramley is moderately susceptible.
The aphid hatches in April at early green cluster from overwintered eggs on the bark and infests the rosette leaves which then curl and develop the characteristic red colour.
The severity of infestation by rosy leaf curling aphid should be determined in each orchard when pre-blossom pest assessments are done at green cluster. At least 25 trees should be inspected for presence/absence of the pest, concentrating on localities where the pest was seen the previous year.
It is hard to distinguish between the rosy leaf curling aphid and the rosy apple aphid but the latter does not cause the characteristic bright red coloration of leaves caused by the rosy leaf curling aphid.
A localised application of an approved insecticide to control the pest should be considered where the pest is detected.
- If only rosy leaf curling, rosy apple or apple grass aphid are to be controlled, then flonicamid (Mainman) is likely to be a good choice as it is a selective aphicide.
- A full approval for spirotetramat (Batavia) on apples for the control of sucking insect pests will control rosy leaf curling aphid, but growers may prefer to reserve its use for more difficult to control pests such as woolly aphid or rosy apple aphid. It must be applied after flowering and works best when pests are moving from brown wood to green tissue. It will prevent population build-up but does not offer pest ‘knockdown’.
- The neonicotinoids acetamiprid (Gazelle) and thiacloprid (Calypso) are also likely to be effective against rosy leaf curling aphid and will control a range of other pests depending on the material chosen.
- Acetamiprid (Gazelle) is the more selective of these materials though its activity against other apple pests has not been explored sufficiently widely. It is known to control mussel scale very effectively when applied at the correct time for the pest i.e. at 90% crawler emergence.
- Thiacloprid (Calypso) is active against a wide range of other important apple pests including rosy apple aphid, apple grass aphid, sawfly, capsids, mussel scale and leaf hoppers. However, it has little activity against woolly aphid and is considered to have some adverse effects on earwigs in orchards if it is used later in the season after blossom when earwigs have populated the tree canopy.
- Earwigs are important natural enemies.
- An emergency authorisation for Movento Top for control of woolly aphid (which lasts until 29 August, 2017) will provide incidental control of rosy leaf curling aphid.
Note that these materials are largely ineffective against winter and tortrix moth caterpillars.
- The synthetic pyrethroid insecticide deltamethrin (Decis) is also approved for control of aphids on apple but its use should be avoided as it is harmful to predatory mites and other insects.
It is important to apply the above insecticides in warm weather conditions at the full recommended dose and in a sufficient spray volume to give adequate cover.
It is also important to apply the insecticide early, before large colonies form which are difficult to control once surrounded by distorted mature leaves.
Insecticides approved for control of aphids on apple
Choice of insecticides – efficacy factors
|Active ingredient||Trade name (examples)||Class||Selectivity||Approved for control of –||Safety to Typhs|
|acetamiprid||Gazelle||neonicotinoid||broad-spectrum, systemic||Aphids and Whitefly||safe|
|deltamethrin||Decis etc.||pyrethroid||broad spectrum||Aphids, codling & tortrix moths||harmful|
|dodecylphenol ethoxylate||Agri 50E||physical acting insecticide||broad spectrum||Aphids, leafhoppers, mealy bugs, spider mites||harmful|
|fatty acids||Savona||soap||broadspectrum||Aphids, scale insects||harmful|
|flonicamid||Teppeki, Mainman||neonicotinoid||selective||Aphids and woolly aphid||safe|
|maltodextrin||Majestik||polysaccharide||broad spectrum||Aphids, spider mites||harmful|
|pyrethrins||Spruzit||extract from pyrethrum||broad spectrum||Aphids, apple blossom weevil, caterpillars, spider mites||harmful|
|spirotetramat||Batavia||tetramic acid derivative||selective||Sucking insect pests||unclassified|
|thiacloprid||Calypso||neonicotinoid||broad-spectrum, systemic||Rosy apple aphid. (Also likely to control capsids and sawfly, though not caterpillars or woolly aphid)||safe|
|Choice of insecticides – Safety factors|
|Hazards||Harvest interval(days)||Max. no. sprays||Buffer zoneWidth (m)|
|Anticholin-Esterase?||Humans||Fish &aquatic life||Bees|
|spirotetramat||no||h, i||y||u||Start of ripening||2||sm|
|h=harmful, i=irritant, d=dangerous, ed=extremely dangerous, t=toxic, c=closed cab required for air assisted sprayers, sm=statutory minimum of 5 m for broadcast airassisted sprayers u=uncategorised/unclassified/unspecified|
Control in organic orchards
In organic orchards the pest should be tolerated except where significant damage is being caused especially to young trees. Thus rosy leaf curling aphid is often ignored or tolerated in organic orchards because of the localised nature of the damage it causes. However, it can become important on some varieties in certain years.
- Cultural methods of control mainly rely on natural enemies, which should be encouraged by providing artificial refuges and flowering plants in and around the orchard.
- Early season sprays of fatty acids (Savona) is the preferred treatment of organic apple growers in the UK for aphids including rosy leaf curling aphid.
- The sprays have to be applied early at the green cluster growth stage (after the overwintered eggs have hatched in spring but before reproduction occurs is best) and in high volumes so that the aphids are thoroughly wetted by the spray.
- Application is sometimes made during gentle rain.